Vacuum forming machine and method of making vacuum formed product

ABSTRACT

A vacuum forming machine according includes a chamber configured to be loaded with a base member and a decorative sheet, a frame arranged to surround the base member that has been loaded into the chamber, a pressure reducer arranged to reduce the pressure inside the chamber, and a communication path arranged to establish communication between the inside of the frame and an external space at the atmospheric pressure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vacuum forming machine for attachinga decorative sheet onto a base member under a reduced pressure and alsorelates to a method of making such a vacuum formed product.

2. Description of the Related Art

Recently, it was proposed, as an alternative decorating technique topainting, that a decorative sheet be attached to the surface of a basemember. A base member decorated with a decorative sheet can be recycledmore easily than a painted one. In addition, the decorated member canhave a different type of fine appearance from that of a painted one,thus contributing to improving its decorativeness, too.

FIG. 20 illustrates an example of a decorative sheet. The decorativesheet 10 shown in FIG. 20 includes a decoration layer 1 and a supportinglayer 2 that supports the decoration layer 1. Examples of the decorationlayer 1 include an ink layer that has been formed by printing and ametal layer that has been formed by depositing a metallic material. Thesupporting layer 2 is made of a resin material such as polyvinylchloride (PVC). When the decorative sheet 10 is attached onto the basemember, an adhesive is applied onto the surface of the decorative sheet10.

Such a decorative sheet 10 is attached onto a base member while thedecorative sheet 10 is being formed under a reduced pressure so as totrace the surface shape of the base member. A vacuum forming machine forforming and attaching a decorative sheet in this manner is disclosed inJapanese Patent Application Laid-Open Publications No. 2006-7422 and No.63-214424, for example.

FIG. 21 illustrates a vacuum forming machine (reduced pressure coatingsystem) 500 as disclosed in Japanese Patent Application Laid-OpenPublication No. 2006-7422. The vacuum forming machine 500 includes achamber box 521, of which the internal pressure can be increased anddecreased adaptively. The chamber box 521 consists of an upper chamberbox 522 and a lower chamber box 524.

Inside the upper chamber box 522, a heater 528 is arranged for heating adecorative sheet (skin member) 10. On the other hand, a table 509 formounting a base member (core member) 16 is arranged inside the lowerchamber box 524. The upper and lower chamber boxes 522 and 524 areconnected to a vacuum tank 507 and a compressed air tank 508.

Now, it will be described how to attach the decorative sheet 10 usingsuch a vacuum forming machine 500.

First of all, as shown in FIG. 21, the base member 16 is mounted on thetable 509 inside the lower chamber box 524 and then the decorative sheet10 is put on the upper surface of the lower chamber box 524.

Next, as shown in FIG. 22, the upper chamber box 522 is lowered, therebybringing the upper and lower chamber boxes 522 and 524 into contact witheach other with the decorative sheet 10 sandwiched between them. As aresult, the upper and lower chamber boxes 522 and 524 are closedairtight.

Subsequently, as shown in FIG. 23, the upper and lower chamber boxes 522and 524 are evacuated by establishing communication with the vacuum tank507, thereby creating a reduced pressure state (a near-vacuum very lowpressure state) inside the upper and lower chamber boxes 522 and 524.

Thereafter, as shown in FIG. 24, the decorative sheet 10 is heated withthe heater 528. This heating process is carried out to the point thatthe decorative sheet 10 softens so much that the adhesive applied on thesurface of the decorative sheet 10 has a sufficient degree ofadhesiveness.

Then, as shown in FIG. 25, the table 509 inside the lower chamber box524 is raised, thereby bringing the base member 16 into contact with thedecorative sheet 10.

Next, as shown in FIG. 26, the pressure inside the upper chamber box 522is restored to the atmospheric pressure (with the reduced pressure stillmaintained in the lower chamber box 524), thereby causing the decorativesheet 10 to be pressed against the base member 16 and formed to tracethe surface shape of the base member 16 by taking advantage of thepressure difference between the upper and lower chamber boxes 522 and524.

In this process step, if compressed air is introduced into the upperchamber box 522 by making the upper chamber box 522 communicate to thecompressed air tank 508, the decorative sheet 10 can be pressed morestrongly against the base member 16.

Finally, as shown in FIG. 28, after the pressure inside the lowerchamber box 524 is also restored to the atmospheric pressure, the upperchamber box 522 is raised and the base member coated with the decorativesheet 10 is unloaded. In this manner, a vacuum formed product consistingof the base member 16 and the decorative sheet 10 attached to itssurface can be obtained.

By performing such a vacuum forming process, even a base member with agreat degree of surface unevenness can be decorated easily with abeautiful sheet.

In the vacuum forming machine 500 disclosed in Japanese PatentApplication Laid-Open Publication No. 2006-7422, to prevent a hollowbase member 16 from expanding and bursting or collapsing under therising pressure inside the chamber box 521, there is a communicationhole 504 that maintains communication between the inside of the basemember 16 and the upper chamber box 522. If the base member 16 is not ahollow one, however, a normal vacuum forming process may be carried outwithout using such a communication hole 504.

With the vacuum forming machine 500 disclosed in Japanese PatentApplication Laid-Open Publication No. 2006-7422, however, when heated,the decorative sheet 10 will soften and sag down as indicated by thedashed curve in FIG. 24. If the forming process were carried out withthe decorative sheet 10 sagged in this manner, that sagged portion ofthe decorative sheet 10 could contact with the base member 16 earlierthan the rest of the sheet 10. In that case, the adhesive in thatportion would get cured earlier and could not be stretched sufficientlyand would become swollen when the decorative sheet 10 is stretched afterthat. That is to say, the appearance of the final vacuum formed productwould be ruined by such an unnecessary raised portion. A similar problemwill arise even when a vacuum forming machine (which is a pictureapplier) as disclosed in Japanese Patent Application Laid-OpenPublication No. 63-214424 is used.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention prevent the appearance ofa final vacuum formed product, obtained by vacuum forming process usinga decorative sheet, from being ruined.

A vacuum forming machine according to a preferred embodiment of thepresent invention is designed to attach a decorative sheet onto a basemember under a reduced pressure. The vacuum forming machine preferablyincludes a chamber, which is configured to be loaded with the basemember and the decorative sheet, a frame arranged to surround the basemember that has been loaded into the chamber, a pressure reducerarranged to reduce pressure inside the chamber, and a communication patharranged to establish communication between the inside of the frame andan external space at the atmospheric pressure.

In one preferred embodiment, the vacuum forming machine preferablyfurther includes a valve provided for the communication path and acontroller programmed to control the operating condition of the valve.

In this particular preferred embodiment, the vacuum forming machinefurther includes an elevating mechanism arranged to raise and lower thedecorative sheet with respect to the frame. The controller performs acontrol operation so that the valve will be opened for a specifiedamount of time when the decorative sheet brought by the elevatingmechanism reaches a predefined distance from the frame.

In a specific preferred embodiment, the specified amount of timepreferably is not less than about 1 ms and not more than about 100 ms,for example.

Alternatively or additionally, the predefined distance is about 50 mm orless, for example.

In still another preferred embodiment, the vacuum forming machine mayfurther include a sensor arranged to collect information about thedistance between the decorative sheet and the frame. The controllercontrols the operating condition of the valve based on a result obtainedby the sensor.

In yet another preferred embodiment, the controller performs a controloperation so that the valve will be opened for a specified amount oftime when a certain period of time passes since the elevating mechanismstarted to operate.

In yet another preferred embodiment, the pressure reducer is arranged toexhaust the air from inside of the frame into outside of the machine.

A method of making a vacuum formed product according to anotherpreferred embodiment of the present invention includes the steps ofpreparing a decorative sheet and a base member, and attaching thedecorative sheet onto the base member inside a chamber. The step ofattaching includes the steps of putting the base member into a framethat is arranged inside the chamber, reducing the pressure inside thechamber in which the base member has been loaded, bringing thedecorative sheet toward the frame inside the chamber at the reducedpressure, and maintaining communication between the inside of the frameand an external space at the atmospheric pressure for a specified amountof time when the decorative sheet reaches a predefined distance from theframe.

In one preferred embodiment, the specified amount of time preferably isnot less than about 1 ms and not more than about 100 ms, for example.

In another preferred embodiment, the step of attaching further includesthe step of pressurizing a space that extends over the decorative sheetand opposite to the frame after the step of maintaining communicationhas been carried out.

A vacuum forming machine according to a further preferred embodiment ofthe present invention includes a frame arranged to surround a basemember that has been loaded into a chamber, and a communication patharranged to establish communication between the inside of the frame andan external space at the atmospheric pressure. Thus, if communication isestablished between the inside of the frame at a reduced pressure andthe external space at the atmospheric pressure when the decorative sheetgets close to the frame, the air can be supplied through thecommunication path to the inside of the frame. As a result, since thepressure in the space between the decorative sheet and the base memberrises, the decorative sheet can be expanded upward (i.e., away from thebase member), thus preventing the decorative sheet heated and softenedunder the heat from sagging. Consequently, the fine appearance will notbe ruined. Since the air is supplied to inside of the frame byestablishing communication between the inside of the frame at thereduced pressure and the external space at the atmospheric pressure, thepressure inside the frame can be increased quickly and easily. Inaddition, in the vacuum forming machine according to a preferredembodiment of the present invention, the base member is surrounded withthe frame. That is why just by supplying the air only to the inside ofthe frame, not the entire chamber, sagging of the decorative sheet canbe minimized. Therefore, as the air needs to be supplied in a relativelysmall amount, the decorative sheet will not be cooled by the air toomuch to avoid decreasing the formability of the decorative sheet,either. On top of that, after the air has been supplied through thecommunication path, the pressure can be reduced again by a pressurereducer in a short time, and the decorative sheet can be attachedquickly.

The vacuum forming machine according to a preferred embodiment of thepresent invention preferably further includes a valve provided for thecommunication path, and a controller programmed to control the operatingcondition (i.e., opened/closed state) of the valve. By controlling theoperating condition of the valve using a controller, the communicationpath can be easily switched between the opened and closed states.

The vacuum forming machine according to a preferred embodiment of thepresent invention preferably further includes an elevating mechanismarranged to raise and lower the decorative sheet with respect to theframe. In that case, the controller performs a control operation so thatthe valve will be opened for a specified amount of time when thedecorative sheet brought by the elevating mechanism reaches a predefineddistance from the frame.

To minimize the sagging of the decorative sheet effectively with a smallamount of the air supplied, the valve is preferably not opened until thedecorative sheet gets sufficiently close to the frame. Thus, thepredefined distance is preferably about 50 mm or less, for example.

The vacuum forming machine according to a preferred embodiment of thepresent invention may further include a sensor arranged to collectinformation about the distance between the decorative sheet and theframe. In that case, the controller controls the operating condition ofthe valve based on a result obtained by the sensor.

Alternatively, the controller may also perform a control operation sothat the valve will be opened for a specified amount of time when acertain period of time passes since the elevating mechanism started tooperate.

The valve is preferably opened for not less than about 1 ms and not morethan about 100 ms, for example. The reason is as follows. Specifically,if the valve were opened for less than just about 1 ms, the amount ofthe air supplied could be too small to minimize sagging of thedecorative sheet. On the other hand, if the valve were opened for aslong as more than about 100 ms, then the decorative sheet would not onlybecome excessively swollen thus ruining its appearance, but would alsohave a decreased temperature because it would take a lot of time toreduce the pressure again.

According to a method of making a vacuum formed product according to apreferred embodiment of the present invention, the step of attaching adecorative sheet in a chamber includes the steps of putting a basemember into a frame that is arranged inside the chamber, reducing thepressure inside the chamber in which the base member has been loaded,and bringing the decorative sheet toward the frame inside the chamber atthe reduced pressure. The attaching step of the method of making avacuum formed product according to a preferred embodiment of the presentinvention further includes the step of maintaining communication betweenthe inside of the frame and an external space at the atmosphericpressure for a specified amount of time when the decorative sheetreaches a predefined distance from the frame. By performing thisadditional process step of maintaining communication, the pressure inthe space between the decorative sheet and the base member can beincreased quickly and easily by supplying the air to the inside of theframe. As a result, the decorative sheet can be expanded upward (i.e.,away from the base member), thus preventing the decorative sheet heatedand softened under the heat from sagging. Consequently, the fineappearance will not be ruined. In addition, in the method of making avacuum formed product according to a preferred embodiment of the presentinvention, the base member is surrounded with the frame. That is whyjust by supplying the air only to the inside of the frame, not theentire chamber, sagging of the decorative sheet can be minimized.Therefore, as the air needs to be supplied at a relatively small amount,the decorative sheet will not be cooled by the air too much to avoiddecreasing its formability, either. On top of that, after the air hasbeen supplied by performing the process step maintaining communication,the pressure can be reduced by a pressure reducer in a short time, andthe decorative sheet can be attached quickly.

In the step of maintaining communication, communication is preferablymaintained between the inside of the frame and the external space at theatmospheric pressure for not less than about 1 ms and not more thanabout 100 ms, for example. The reason is as follows. Specifically, ifthe communication were maintained for less than just about 1 ms, theamount of the air supplied could be too small to minimize sagging of thedecorative sheet. On the other hand, if the communication weremaintained for as long as more than about 100 ms, then the decorativesheet would not only become excessively swollen thus ruining itsappearance, but also would have a decreased temperature because it wouldtake a lot of time to reduce the pressure again.

The step of attaching preferably further includes the step ofpressurizing a space that extends over the decorative sheet and oppositeto the frame after the step of maintaining communication has beencarried out. By performing such an additional process step ofpressurizing, the pressure difference that will cause the decorativesheet to be pressed against the base member can be further increased andtherefore the decorative sheet can be attached even more quickly.

According to various preferred embodiments of the present invention, avacuum formed product, which is obtained by vacuum forming process usinga decorative sheet, will prevent its appearance from being ruined.

Other features, elements, processes, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of preferred embodiments of the presentinvention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a vacuum forming machine 100 accordingto a specific preferred embodiment of the present invention.

FIG. 2 is a perspective view schematically illustrating a frame for usein the vacuum forming machine 100.

FIG. 3 schematically illustrates a vacuum forming machine 100 accordingto an alternative preferred embodiment of the present invention.

FIG. 4 schematically illustrates a vacuum forming machine 100 accordingto another alternative preferred embodiment of the present invention.

FIGS. 5 through 11 illustrate respective manufacturing process steps tomake a vacuum formed product using the vacuum forming machine 100.

FIG. 12 is a graph showing how the pressure in the upper box and thepressure inside the frame change with time after having started to bereduced in the attaching step.

FIG. 13 is a flowchart illustrating a detailed procedure of theattaching step.

FIG. 14 is a flowchart illustrating an alternative detailed procedure ofthe attaching step.

FIG. 15 shows the temperature dependence of the storage moduli E′ thatwere obtained by measuring the dynamic viscoelasticity of polyvinylchloride, polymethyl methacrylate and polycarbonate.

FIG. 16 schematically illustrates a vacuum forming machine 100 accordingto another preferred embodiment of the present invention.

FIG. 17 schematically illustrates a vacuum forming machine 100 accordingto still another preferred embodiment of the present invention.

FIG. 18 schematically illustrates a vacuum forming machine 100 accordingto yet another preferred embodiment of the present invention.

FIG. 19 schematically illustrates a vacuum forming machine 100 accordingto yet another preferred embodiment of the present invention.

FIG. 20 illustrates an example of a decorative sheet 10.

FIGS. 21 through 28 illustrate respective manufacturing process steps tomake a vacuum formed product using a conventional vacuum forming machine500.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings. It should benoted, however, that the present invention is in no way limited to thespecific preferred embodiments to be described below.

FIG. 1 illustrates a vacuum forming machine 100 according to a specificpreferred embodiment of the present invention. In FIG. 1, a decorativesheet 10 and a base member 16 are also shown to make this descriptionmore easily understandable. The vacuum forming machine 100 is used toattach the decorative sheet 10 (which will be simply referred to hereinas a “sheet”) onto the base member 16 under a reduced pressure. That isto say, the vacuum forming machine 100 is an apparatus for making avacuum formed product including the base member 16 and the decorativesheet 10 that has been attached onto the surface of the base member 16.

As already described with reference to FIG. 20, the decorative sheet 10includes a decoration layer 1 and a supporting layer 2 that supports thedecoration layer 1. The decoration layer 1 may be either an ink layerformed by printing or a metal layer formed by depositing a metallicmaterial. The supporting layer 2 is made of a resin material such aspolycarbonate or polyethylene terephthalate. When the sheet 10 isattached onto the base member 16, an adhesive is applied onto thesurface of the sheet 10. In the following description, the supportinglayer 2 that forms the body of the sheet 10 will be referred to hereinas a “sheet base member”. The base member 16 (which forms the body ofthe vacuum formed product) may be made of a resin material, a metallicmaterial or any other suitable material.

As shown in FIG. 1, the vacuum forming machine 100 of this preferredembodiment preferably includes a chamber (i.e., a vacuum vessel) 20,which is configured to be loaded with the base member 16 and the sheet10, a frame 30 arranged to surround the base member 16 that has beenloaded into the chamber 20, a pressure reducer 40 arranged to reduce thepressure inside the chamber 20, and a communication path 50 arranged toestablish communication between the inside of the frame 30 and theexternal space at the atmospheric pressure. The vacuum forming machine100 further includes a holder 60 arranged to hold the sheet 10 insidethe chamber 20.

The chamber 20 is partitioned by the sheet 10 and the holder 60 into anupper box 21 and a lower box 22. The upper box 21 has an opening at thebottom, while the lower box 22 has an opening at the top. And the basemember 16 is put on the bottom of the lower box 22.

The chamber 20 of this preferred embodiment further includes a heaterbox 23 that houses a heater 70 arranged to heat the sheet 10. The heater70 may be a far infrared heater, for example. The heater box 23 isarranged adjacent to the lower box 22. When heating the sheet 10, theheater 70 is introduced into the lower box 22.

The frame 30 is arranged inside the lower box 22. More specifically, theframe 30 is put on the bottom surface of the lower box 22. The frame 30preferably has a cylindrical shape (e.g., a rectangular cylindricalshape in this preferred embodiment) as shown in FIG. 2, and the basemember 16 is put into the space 30A inside the frame 30. As shown inFIG. 1, the frame 30 extends from the bottom surface of the lower box 22to reach a higher level than the top of the base member 16. In otherwords, the top of the frame 30 is located higher than that of the basemember 16. The frame 30 may be made of a resin material such aspolypropylene (PP), polytetrafluoroethylene (PTFE) or polyethylene (PE)or a metallic material such as aluminum. The top of the frame 30 ispreferably higher than that of the base member 16 by at least about 10mm (e.g., approximately 20 mm). This is because if the difference inheight between the respective tops of the frame 30 and the base member16 were less than about 10 mm, then the sheet 10 could not be attachedto the base member 16 just as intended and the final vacuum formedproduct could have its appearance marred.

The pressure reducer 40 is typically a vacuum pump. A first valve 41arranged to adjust the degree of pressure reduction inside the upper box21 is provided between the pressure reducer 40 and the upper box 21. Theair inside the upper box 21 is exhausted through the first valve 41. Onthe other hand, a second valve 42 arranged to adjust the degree ofpressure reduction inside the lower box 22 is provided between thepressure reducer 40 and the lower box 22. The air inside the lower box22 is exhausted through the second valve 42. Specifically, the air isexhausted from inside of the frame 30.

The communication path 50 preferably includes the inner space of acommunication tube 51 that connects the inside of the frame 30 and theexternal space together, and is provided with a third valve 52. When thethird valve 52 is opened, the communication path 50 establishescommunication between the inside of the frame 30 and the external space.On the other hand, when the third valve 52 is closed, the inside of theframe is isolated from the external space. In this preferred embodiment,the operating condition (i.e., opened/closed state) of the third valve52 is preferably controlled by the controller 54. In other words, thevacuum forming machine 100 includes a controller 54 programmed tocontrol the operating condition of the third valve 52.

The controller 54 of this preferred embodiment preferably controls notonly the operating condition of the third valve 52 on the communicationpath 50 but also that of the first valve 41 arranged between thepressure reducer 40 and the upper box 21 and that of the second valve 42arranged between the pressure reducer 40 and the lower box 22. Thecontroller 54 may be implemented as a microcomputer, for example.

The holder 60 preferably includes a ring-shaped (such as square ring)member that can hold and grip the periphery of the sheet 10 and that canbe raised or lowered vertically while holding the sheet 10. That is tosay, the holder 60 functions as an elevating mechanism to raise andlower the sheet 10 with respect to the frame 30 (or the base member 16).

As described above, the vacuum forming machine 100 of this preferredembodiment includes the frame 30, which surrounds the base member 16that has been loaded into the chamber 20, and the communication path 50arranged to establish communication between the inside of the frame 30and the external space at the atmospheric pressure. Thus, ifcommunication is established between the inside of the frame 30 at areduced pressure and the external space at the atmospheric pressure whenthe sheet 10 gets close to the frame 30, the air can be supplied throughthe communication path 50 to the inside of the frame 30. As a result,since the pressure in the space between the sheet 10 and the base member16 rises, the sheet 10 can be expanded upward (i.e., away from the basemember 16), thus preventing the sheet heated and softened under the heatfrom sagging. Consequently, the fine appearance will not be ruined orthe sheet will not be attached imperfectly, either.

The pressure inside the frame 30 could be increased (i.e., restored toan ordinary pressure) even by controlling the operating condition of thesecond valve 42 between the lower box 22 and the pressure reducer 40. Inthat case, however, it would be difficult to quickly raise the pressurehigh enough to reduce sagging of the sheet 10 sufficiently. In thevacuum forming machine 100 of this preferred embodiment, on the otherhand, the air is supplied to the inside of the frame 30 by establishingcommunication between the inside of the frame 30 at a reduced pressureand the external space at the atmospheric pressure, and therefore, thepressure inside the frame 30 can be increased easily and quickly.

In addition, in the vacuum forming machine 100 of this preferredembodiment, the base member 16 is surrounded with the frame 30. That iswhy just by supplying the air only to the inside of the frame 30, notthe entire chamber 20, sagging of the sheet 10 can be minimized.Therefore, as the air needs to be supplied at a relatively small amount,the sheet 10 will not be cooled by the air too much to avoid decreasingthe formability of the sheet 10, either. On top of that, after the airhas been supplied through the communication path 50, the pressure can bereduced again by the pressure reducer 40 in a short time, and the sheet10 can be attached quickly.

The vacuum forming machine 100 preferably includes the third valve 52provided for the communication path 50 and the controller 54 arranged tocontrol the operating condition of the third valve 52 as in thepreferred embodiment described above. By controlling the operatingcondition of the third valve 52 using the controller 54, thecommunication path 50 can be easily switched between the opened andclosed states.

The vacuum forming machine 100 of this preferred embodiment furtherincludes an elevating mechanism (i.e., the holder 60) to raise and lowerthe sheet 10 with respect to the frame 30. The controller 54 performs acontrol operation so that the third valve 52 will be opened for aspecified amount of time when the sheet 10 brought down by the holder 60functioning as an elevating mechanism reaches a predefined distance fromthe frame 30. To minimize the sagging of the sheet 10 effectively with asmall amount of the air supplied, the third valve 52 is preferably notopened until the sheet 10 gets sufficiently close to the frame 30.Specifically, when the third valve 52 is opened, the distance betweenthe sheet 10 and the frame 30 is preferably 50 mm or less, morepreferably 30 mm or less.

Information about the distance between the sheet 10 and the frame 30 maybe collected by a sensor 28 arranged inside the chamber 20 as shown inFIG. 3, for example. In that case, the controller 54 controls theoperating condition of the third valve 52 based on a result obtained bythe sensor 28. That is to say, on determining, based on a resultobtained by the sensor 28, that the sheet 10 has reached a predefineddistance from the frame 30, the controller 54 performs a controloperation so that the third valve 52 will be opened for a specifiedamount of time.

Any of various kinds of distance sensors or proximity sensors may beused as the sensor 28. Alternatively, a photoelectric tube sensor mayalso be used. If a photoelectric tube sensor is used as the sensor 28, atransmitter 28 a and a receiver 28 b are preferably arranged at apredetermined height so as to face each other as shown in FIG. 4. Andwhen the signal transmitted by the transmitter 28 a discontinues (i.e.,no longer received at the receiver 28 b), it is determined that thesheet 10 and the holder 60 have reached a predetermined height (i.e.,are now located between the transmitter 28 a and the receiver 28 b). Asthe photoelectric tube sensor, a beam sensor NX5-M10RA produced by SunxLimited may be used, for example.

Alternatively, the controller 54 may also control the operatingcondition of the valve 52 according to the amount of time that haspassed since the holder 60 (and the sheet 10) started to be lowered,instead of the distance between the sheet and the frame 30. In otherwords, the controller 54 may perform a control operation so that thethird valve 52 will be opened for a specified amount of time when acertain period of time passes since the elevating mechanism (i.e., theholder 60 in this example) started to operate. For example, thecontroller 54 may perform a control operation so that the third valve 52will be opened one second after the holder 60 started to be lowered.

The third valve 52 is preferably opened for not less than about 1 ms andnot more than about 100 ms, for example. The reason is as follows.Specifically, if the third valve 52 were opened for less than just about1 ms, the amount of the air supplied could be too small to minimizesagging of the sheet 10. On the other hand, if the third valve 52 wereopened for as long as more than about 100 ms, then the sheet 10 wouldnot only become too swollen to avoid ruining its appearance, but alsohave its temperature and degree of formability decreased because itwould take a lot of time to reduce the pressure again.

Next, it will be described how to make a vacuum formed product using thevacuum forming machine 100 described above. The manufacturing process ofthis preferred embodiment includes at least the step of preparing thesheet 10 and the base member 16 and the step of attaching the sheet 10onto the base member 16 in the chamber 20 while forming the sheet 10.

Hereinafter, the manufacturing process will be described in detail withreference to FIGS. 5 through 11, which are cross-sectional viewsillustrating respective process steps to make a vacuum formed product.It should be noted that in FIGS. 5 to 11, some members of the vacuumforming machine 100 are not illustrated.

First of all, the sheet 10 and the base member 16 are prepared (thisprocess step will be referred to herein as a “preparing step”). Asdescribed above, the sheet 10 includes a decoration layer 1 and a sheetbase member (supporting layer) 2 that supports the decoration layer 1.The decoration layer 1 may be either an ink layer formed by printing ora metal layer formed by depositing a metallic material, for example. Thedecoration layer 1 does not have to be a single layer but may also havea multilayer structure in which an ink layer, a metal layer, and otherlayers have been stacked one upon the other. The sheet base member 2preferably is made of a resin material such as polycarbonate orpolyethylene terephthalate, for example. The base member 16 is typicallymade of a resin material as described above but may also be made of ametallic material or any other suitable material. The base member 16 canbe made by any known process. For example, the base member 16 may bemade of a resin material by injection molding process. As the resinmaterial, an ABS resin or an AES resin is generally preferred but nylonis preferably used in view of its thermal resistance. Also, taking theenvironmental issues into consideration, an olefin-based recycledmaterial or polyethylene is preferably used.

Next, the sheet 10 is attached onto the base member 16 while beingstretched (i.e., formed). This process step will be referred to hereinas an “attaching step”. Specifically, first, the base member 16 is putinto the frame 30 that is arranged inside the chamber 20 as shown inFIG. 5. More specifically, the base member 16 is mounted onto the bottomsurface of the lower box 22 so as to be surrounded with the frame 30. Inthis case, the top of the frame 30 is located at a higher level thanthat of the base member 16 mounted.

Subsequently, as shown in FIG. 6, the sheet 10 is fixed onto the holder11. In process step, an adhesive has been applied to one of the twosurfaces of the sheet 10.

Thereafter, as shown in FIG. 7, the sheet 10 is heated with the heater70. To soften the sheet 10 sufficiently, the sheet 10 is preferablyheated to a temperature falling within the range of approximately(T_(A)−40)° C. to (T_(A)+50)° C., more preferably to a temperaturefalling within the range of approximately (T_(A)+30)° C. to (T_(A)+50°C.), where T_(A) indicates the load deflection temperature of the sheetbase member 2. Also, in this process step, the pressure inside thechamber 20, i.e., inside the upper and lower boxes 21 and 22, isreduced.

Next, as shown in FIG. 8, the sheet 10, as well as the holder 60, isbrought down toward the frame 30. And when the sheet 10 reaches apredefined distance from the frame 30, communication is establishedbetween the inside of the frame 30 and the external space at theatmospheric pressure and maintained for a specified amount of time asshown in FIG. 9. By establishing communication between the inside of theframe 30 and the external space, the air is supplied from the externalspace into the frame 30. As a result, the pressure in the space insidethe frame 30 (i.e., the space between the sheet 10 and the base member16) rises and the sheet 10 becomes expanded upward (i.e., away from thebase member 16) as shown in FIG. 9.

Thereafter, when the sheet 10 is brought down to the point that thesheet 10 contacts with the frame 30 (and when the communication betweenthe inside of the frame 30 and the external space is discontinued justbefore or after that), the sheet 10 is pressed against, and bonded to,the base member 16 as shown in FIG. 10 because the pressure is stillkept low. During this bonding, the sheet 10 is attached while beingformed so as to trace the surface shape of the base member 16.

After that, excessive portions of the sheet 10 (i.e., portions that donot cover the base member 16 but extend over the member 16) are cut off(or trimmed) with some cutter such as a rotary blade, thereby completinga vacuum formed product 19 including the base member 16 and thedecorative sheet 10 that has been attached onto the surface of the basemember 16 as shown in FIG. 11.

In the manufacturing process of this preferred embodiment, the attachingstep includes the steps of putting the base member 16 into the frame 30that is arranged inside the chamber 20, reducing the pressure inside thechamber 20 in which the base member 16 has been loaded, and bringing thesheet 10 toward the frame 30 inside the chamber 20 at the reducedpressure. The attaching step of the manufacturing process of thispreferred embodiment further includes the step of maintainingcommunication between the inside of the frame 30 and the external spaceat the atmospheric pressure for a specified amount of time when thesheet 10 reaches a predefined distance from the frame 30.

By performing this additional process step of maintaining communication,the pressure in the space between the sheet 10 and the base member 16can be increased quickly and easily by supplying the air to the insideof the frame 30. As a result, the sheet 10 can be expanded upward (i.e.,away from the base member 16), thus preventing the sheet 10 heated andsoftened under the heat from sagging. Consequently, the fine appearancewill not be ruined.

In addition, in the manufacturing process of this preferred embodiment,the base member 16 is surrounded with the frame 30. That is why just bysupplying the air only to the inside of the frame 30, not the entirechamber 20, sagging of the sheet 10 can be minimized. Therefore, as theair needs to be supplied at a relatively small amount, the sheet 10 willnot be cooled by the air too much to avoid decreasing its formability,either. On top of that, after the air has been supplied by performingthe process step of maintaining communication, the pressure can bereduced again by the pressure reducer 40 in a short time, and the sheet10 can be attached quickly.

The step of attaching preferably further includes the step ofpressurizing a space that spreads over the sheet 10 and opposite to theframe 30 after the step of maintaining communication has been carriedout. By performing such an additional process step of pressurizing, thepressure difference that will cause the sheet 10 to be pressed againstthe base member can be further increased and therefore the sheet 10 canbe attached even more quickly. This process step of pressurizing may becarried out by supplying compressed air from a compressor (not shown)into the upper box 21, for example.

FIG. 12 shows how the pressure inside the chamber 20 changes with timeafter having started to be reduced in the attaching step. In FIG. 12,the pressure inside the upper box 21 is indicated by the solid curve,while the pressure inside the frame 30 is indicated by the dashed curve.

As shown in FIG. 12, after the pressure has started to be reduced, thepressures inside the upper box 21 and inside the frame 30 fall in asimilar pattern for a while. Specifically, the pressures inside theupper box 21 and inside the frame 30 fall to a gauge pressure (that isthe difference from the atmospheric pressure) of about −90 kPa to about−100 kPa.

Next, the sheet 10 starts to be lowered. And when the sheet 10 reaches apredefined distance from the frame 30, communication is establishedbetween the inside of the frame 30 and the external space. As a result,the pressure inside the frame 30 becomes higher than the pressure insidethe upper box 21 preferably by more than 0 Pa but equal to or smallerthan about 0.1 kPa. This is because if the pressure difference exceededabout 0.1 kPa, the sheet 10 might be swollen too much to avoid ruiningits appearance.

Then, after the sheet 10 has contacted with the frame 30, the pressureinside the upper box 21 becomes higher than the pressure inside theframe 30. Consequently, the sheet 10 becomes pressed against the basemember 16 heavily and becomes bonded to the base member 16 quickly.

Hereinafter, the attaching step will be described in further detail withreference to FIG. 13, which is a flowchart showing more detailed processsteps of the attaching step.

By turning switch of the vacuum forming machine 1000N, the attachingstep starts. After that, first of all, the pressure reducer 40 (which istypically a vacuum pump) is driven in Step S1.

Next, it is determined in Step S2 whether or not pressure reduction (orevacuation) has been finished. This decision is made based on a resultobtained by a number of pressure sensors for detecting the pressuresinside the upper and lower boxes 21 and 22. If the pressure valuedetected by the pressure sensors is equal to or smaller than apredetermined value (of about −95 kPa or less), it is determined thatthe pressure reduction has been finished.

Until the pressure reduction is done, the first and second valves 41 and42 are operated in a predetermined pattern that is stored in thecontroller 54 (in Step S3). Specifically, the first and second valves 41and 42 are controlled to be opened to a target degree at a predeterminedrate and then maintain their target degree of opening. The rate ofopening the first and second valves 41 and 42 and their target degree ofopening have been determined in advance so that the pressure differencebetween the upper and lower boxes 21 and 22 falls within a predeterminedrange (about 3 kPa or less, for example).

This process step S3 will be performed a number of times until thepressure reduction is completed. By starting the process step S3, thedegrees of opening of the first and second valves 41 and 42 start toincrease and the pressures inside the upper and lower boxes 21 and 22fall to about −90 kPa to about −100 kPa. Optionally, when the processstep S3 is carried out for the second time and on, the rate of openingthe first and second valves 41 and 42 and their target degree of openingmay be adjusted based on a result obtained by the pressure sensors.

And when the pressure reduction is done, the heater 70 is turned ON,thereby starting to heat the sheet 10 with the heater 70 (in Step S4).As a result, the temperature of the sheet 10 starts to rise.

Next, it is determined in Step S5 whether or not the temperature of thesheet 10 is equal to or higher than a preset one. This decision is madebased on a result obtained by a temperature sensor (e.g., an infraredsensor) arranged to sense the temperature of the sheet 10. As usedherein, the “preset temperature” is a preferred forming temperature atwhich the sheet 10 softens sufficiently. If the sheet base member 2 ismade of polycarbonate, the preset temperature may be approximately 190°C., for example.

Until the temperature of the sheet 10 reaches the preset one, the firstand second valves 41 and 42 are operated as in the process step S3 in apredetermined pattern that is stored in the controller 54 (in Step S6).

And when the temperature of the sheet 10 reaches the predefined one ormore, the heater 70 is turned OFF to end the heating process using theheater 70 (in Step S7).

Thereafter, the holder 60 is lowered to a predetermined degree, therebybringing the sheet 10 down in Step S8. In this process step, the holder60 may be lowered until the sheet 10 contacts with the frame 30, forexample.

Next, it is determined in Step S9 whether or not a predetermined amountof time (of one second, for example) has passed since the holder 60started to be lowered.

When the predetermined amount of time passes, the third valve 52 will beopened for a specified amount of time (which is preferably not less thanabout 1 ms and not more than about 100 ms) in Step S10. As a result, theair is supplied from the external space to the inside of the frame 30through the communication path 50 and the pressure inside the frame 30rises. Meanwhile, since the pressure reduction (or evacuation) using thesecond valve 42 is still continued, the air supplied is soon exhaustedand the pressure inside the frame 30 that has once temporarily risenfalls quickly. As a result, it is possible to avoid an unwantedsituation where the air remains between the attached sheet 10 and thebase member 16.

Thereafter, the first valve 41 is closed fully in Step S11 andcompressed air is supplied into the upper box 21 using a compressor (inStep S12). As a result, the pressure inside the upper box 21 becomeshigher than the one inside the frame 30.

After the pressure inside the upper box 21 has been increased toapproximately 200 kPa, for example, the next process step needs to waita predetermined amount of time for the sheet to be attached just asintended. For that purpose, it is determined in Step S13 whether or nota predetermined amount of time (of two seconds, for example) has passedsince the pressure was increased.

When the predetermined amount of time passes, the second valve 42 isclosed fully in Step S14 and the pressure reducer 40 is stopped in StepS15.

Thereafter, the upper and lower boxes 21 and 22 are opened to the air(in Step S16). As a result, the pressures inside the upper and lowerboxes 21 and 22 become equal to the atmospheric pressure and theattaching step ends.

In the flowchart shown in FIG. 13, the controller 54 controls theoperating condition of the third valve 52 based on the amount of timethat has passed since the holder 60 started to be lowered, anddetermines in Step S9 whether or not a specified amount of time haspassed since the holder 60 started to be lowered. However, thecontroller 54 may also control the operating condition of the thirdvalve 52 by reference to (information about) the distance between thesheet 10 and the frame 30 as described above. In that case, as shown inFIG. 14, it is determined in Step S9 whether or not the distance betweenthe sheet 10 and the frame 30 is equal to or smaller than a predefinedone (about 50 mm, for example).

As described above, according to various preferred embodiments of thepresent invention, it is possible to prevent a vacuum formed product,which is being manufactured by vacuum forming process using thedecorative sheet 10, from having its appearance ruined. Preferredembodiments of the present invention are applicable to a vacuum formingprocess that uses any of various kinds of decorative sheets 10. Amongother things, preferred embodiments of the present invention can be usedparticularly effectively when the decorative sheet 10 needs to be formedat a relatively high temperature and within a narrow temperature range.

The preferred temperature range for forming the decorative sheet 10varies according to the resin material of the sheet base member 2. FIG.15 shows the temperature dependence of the storage moduli E′(corresponding to the moduli of elasticity) that were obtained bymeasuring the dynamic viscoelasticity of polyvinyl chloride (PVC),polymethylmethacrylate (PMMA) and polycarbonate (PC).

The decorative sheet 10 is preferably formed at such a temperature atwhich the sheet base member 2 has a storage modulus E′ of about 100 MPaor less, for example. That is to say, according to the curvesrepresenting the moduli of elasticity shown in FIG. 15, the broader thetemperature range in which the storage modulus is preferably about 100MPa or less (which will be referred to herein as a “formable range”),i.e., the less steep its gradient, and the closer to lower temperaturesthe temperature range, the more easily the forming process should bedone. As can be seen from FIG. 15, the formable range of PVC is fromabout 50° C. through about 90° C. but those of PMMA and PC are fromabout 120° C. through about 170° C. and from about 170° C. through about200° C., respectively. These results reveal that if the sheet basemember 2 is made of PMMA, the vacuum forming process is more difficultto be done than a situation where the sheet base member 2 is made ofPVC. Also, if the sheet base member 2 is made of PC, the vacuum formingprocess is even more difficult to complete. That is to say, advantagesof preferred embodiments of the present invention will be especiallyadvantageous if the sheet base member 2 is made of a material, of whichthe formable range has a relatively high lower limit (more specifically,if the sheet base member 2 is made of a material of which the formablerange has a lower limit of about 150° C. or more (e.g., PC).

The conventional vacuum forming machine does not perform a control suchthat when the sheet 10 reaches a predefined distance from the basemember 16, the space between the sheet 10 and the base member 16 has itspressure increased momentarily. This is because the conventional vacuumforming machine supposes the sheet base member 2 to be made of easilyformable PVC. According to a preferred embodiment of the presentinvention, on the other hand, even if the sheet base member 2 is made ofPC that is rather difficult to form, the vacuum forming process can alsobe done just as intended.

It should be noted that the configuration for maintaining communicationbetween the inside of the frame 30 and the external space does not haveto be the one shown in FIG. 1. An alternative configuration for thevacuum forming machine 100 of this preferred embodiment is shown in FIG.16. In the configuration shown in FIG. 1, the communication path 50arranged to establish and maintain communication between the inside ofthe frame 30 and the external space is provided totally independently ofthe vacuum path to reduce the pressure inside the lower box 22. On theother hand, in the configuration shown in FIG. 16, a portion 43 a of thecommunication path 43 arranged to establish and maintain communicationbetween the lower box 22 and the pressure reducer 40 also functions as aportion of the communication path 50 to maintain communication betweenthe inside of the frame 30 and the external space. Even if such aconfiguration is adopted, the air can still be supplied into the frame30 and sagging of the sheet 10 can also be minimized.

In the preferred embodiments described above, the holder is preferablyarranged to function as an elevating mechanism (i.e., the sheet 10 ispreferably lowered along with the holder 60). Conversely, the basemember 16 and the frame 30 may be raised. In that case, a table (or asupporting stage) 80 that supports the base member 16 and the frame 30may be arranged inside the lower box 22 and the base member 16 and theframe 30 may be raised along with that table 80 using a hydrauliccylinder 81 as shown in FIG. 17.

Furthermore, in FIG. 1 and other drawings, only one base member 16 ispreferably loaded into the frame 30. Alternatively, a number of basemembers 16 may be loaded into the frame 30 as shown in FIG. 18. Byloading a number of base members 16 at a time into the frame 30, morevacuum formed products 19 can be obtained per attaching step, andtherefore, the manufacturing cost can be reduced.

Furthermore, in the preferred embodiments described above, the chamber20 preferably includes a heater box 23. However, the present inventionis in no way limited to that specific preferred embodiment.Alternatively, the heater 70 may be arranged inside the upper box 21 andthe heater box 23 may be omitted as shown in FIG. 19.

A vacuum formed product 19 made by the manufacturing process accordingto a preferred embodiment of the present invention has a fine appearanceand can be used effectively as an exterior member for various types oftransportation vehicles. The formed product can be used effectively asthe tank housing, front fender or tail cowl of a motorcycle, forexample.

According to various preferred embodiments of the present invention, itis possible to prevent the appearance of a vacuum formed product,obtained by performing a vacuum forming process using a decorativesheet, from being ruined and also prevent the decorative sheet frombeing attached imperfectly during that process.

A vacuum formed product obtained with the vacuum forming machineaccording to various preferred embodiments of the present invention orby the method of making a vacuum formed product according to otherpreferred embodiments the present invention has such a fine appearanceso as to be used effectively as an exterior member for various types oftransportation vehicles including passenger cars, buses, trucks,motorcycles, tractors, airplanes, motorboats, and civil engineeringvehicles.

While the present invention has been described with respect to preferredembodiments thereof, it will be apparent to those skilled in the artthat the disclosed invention may be modified in numerous ways and mayassume many embodiments other than those specifically described above.Accordingly, it is intended by the appended claims to cover allmodifications of the invention that fall within the true spirit andscope of the invention.

This application is based on Japanese Patent Application No. 2008-333755filed on Dec. 26, 2008, the entire contents of which are herebyincorporated by reference.

1. A vacuum forming machine for attaching a decorative sheet onto a basemember, the vacuum forming machine comprising: a chamber configured tobe loaded with the base member and the decorative sheet; a framearranged to surround the base member that has been loaded into thechamber; a pressure reducer arranged to reduce pressure inside thechamber; and a communication path arranged to establish communicationbetween an inside of the frame and an external space at atmosphericpressure.
 2. The vacuum forming machine of claim 1, further comprising avalve provided in the communication path, and a controller programmed tocontrol an operating condition of the valve.
 3. The vacuum formingmachine of claim 2, further comprising an elevating mechanism arrangedto raise and lower the decorative sheet with respect to the frame,wherein the controller is programmed to perform a control operation sothat the valve will be opened for a specified amount of time when thedecorative sheet brought by the elevating mechanism reaches a predefineddistance from the frame.
 4. The vacuum forming machine of claim 3,wherein the specified amount of time is not less than about 1 ms and notmore than about 100 ms.
 5. The vacuum forming machine of claim 3,wherein the predefined distance is about 50 mm or less.
 6. The vacuumforming machine of claim 3, further comprising a sensor arranged tocollect information about the distance between the decorative sheet andthe frame, wherein the controller is programmed to control the operatingcondition of the valve based on a result obtained by the sensor.
 7. Thevacuum forming machine of claim 3, wherein the controller is programmedto perform a control operation so that the valve will be opened for aspecified amount of time when a certain period of time passes since theelevating mechanism started to operate.
 8. The vacuum forming machine ofclaim 1, wherein the pressure reducer is arranged to exhaust air frominside of the frame to outside of the machine.
 9. A method of making avacuum formed product, the method comprising the steps of: preparing adecorative sheet and a base member; and attaching the decorative sheetonto the base member inside a chamber; wherein the step of attachingincludes the steps of: (a) putting the base member into a frame that isarranged inside the chamber; (b) reducing pressure inside the chamber inwhich the base member has been loaded; (c) bringing the decorative sheettoward the frame inside the chamber at the reduced pressure; and (d)maintaining communication between an inside of the frame and an externalspace at atmospheric pressure for a specified amount of time when thedecorative sheet reaches a predefined distance from the frame.
 10. Themethod of claim 9, wherein the specified amount of time is not less thanabout 1 ms and not more than about 100 ms.
 11. The method of claim 9,wherein the step of attaching further includes a step (e) ofpressurizing a space that extends over the decorative sheet and oppositeto the frame after the step (d) has been carried out.